Explosively formed projectiles (“EFP”) (also known as explosively formed penetrators, and explosively formed perforators) are provided by so-called “shaped charges” that utilize explosive energy to deform a liner disposed over a concave-shaped explosive material into a coherent projectile while simultaneously accelerating it to extremely high velocities. An EFP offers a method of employing a kinetic energy projectile without the use of a large gun. A conventional EFP device is comprised of a metallic liner, a case, an explosive material, and an initiator. The case may also contain a retaining ring to position and hold the liner-explosive subassembly in place. EFP devices are normally designed to produce a single massive, high-velocity projectile that has a high kinetic energy capable of penetrating solid objects, such as, for example, a target in the form of an armored vehicle or a subterranean formation. Upon detonation, the explosive material creates enormous pressures that accelerate the liner while simultaneously reshaping it into a projectile of a rod-like or other desired shape. On impact with a target, the EFP delivers a high mechanical power in an extremely focused manner, enabling penetration of target materials that are impervious to conventional explosives.
The liner of the EFP device is formed from a solid material that is formed into a projectile responsive to detonation of the explosive charge. The liner material is typically a high-density, ductile material, such as a metal, a metal alloy, a ceramic, or a glass. The metals commonly used in liners include iron, copper, aluminum, molybdenum, depleted uranium, tungsten, and tantalum. Depending on the mechanical strength characteristics of the target, penetration by the liner may heavily damage or destroy the target in the vicinity of impaction by the projectile formed from the liner. However, if the target is an armored vehicle or other heavily armored target, the liner may not cause the desired degree of damage. The destructive capability of the EFP may be limited by the geometry and weight of the projectile formed from the liner by the EFP device and the velocity imparted to the projectile by the detonation of the explosive material. Further, aerodynamic drag will generally act to decrease the velocity of projectile as the projectile travels toward the target.
In some applications, in order to improve the destructive capability of the warhead, the liner may be provided with the ability to produce secondary reactions that cause additional damage. These secondary reactions commonly include incendiary reactions. As disclosed in U.S. Pat. No. 4,807,795 to LaRocca et al., pyrophoric metals are added to the liner to provide the desired incendiary effects. In LaRocca et al., a double-layered liner is disclosed, where a layer of dense metal provides the penetration ability and a layer of light metal, such as aluminum or magnesium, produces the incendiary effects.
While metals have been commonly used in liners, reactive materials have also been used. Upon impact with a target, the reactive material of the liner produces a high burst of energy. Such reactive materials for use in penetrating warheads are disclosed, for example, in U.S. Pat. No. 6,962,634, issued Nov. 8, 2005, entitled “Low Temperature, Extrudable, High Density Reactive Materials” and assigned to the assignee of the present invention, the entire disclosure of which patent is incorporated herein by this reference.